Due to environmental pollution and the shortage of petroleum resources, environmentally friendly renewable biochemical products have been of interesting interest, and studies thereon have been actively conducted. Particularly, many studies have recently been conducted to produce biochemical products, which can replace petrochemical products, from fermentable sugar based on microbial metabolic engineering. The cost-effective production of fermentable sugar, the development of microbial metabolic engineering and genetic engineering technology, and processes for the separation and purification of final products are considered the key technical factors for success in the development of such biochemical products.
In addition, if biochemical products can be produced at high concentrations, costs for separation and purification processes in subsequent stages can be reduced, thereby ensuring the price competitiveness of the final biochemical products. If cellulose-, lignocelluloses-, corn- or starch based biomass is used as a substrate at a high ratio, a high concentration of fermentable sugar can be produced. Thus, if such fermentable sugar is used as a raw material, high concentrations of biochemical products can be produced. Particularly, biochemical products are produced by fermentation processes in which a large amount of water is used, leading to an increase in the size of a reactor and an increase in energy consumption in the final isolation process, which adversely affect the price competitiveness of the final products.
U.S. Pat. No. 5,733,758 discloses a vertical tower type plug flow reactor for the saccharifying and fermenting pretreated biomass. In the invention disclosed in the above-described US patent, sugar is obtained by fermenting biomass using a multistage plug-flow reactor, but there are disadvantages in that, because mixing is performed using an additional mixer, the overall size of the system is large, and because a mixer is used to mix highly viscous sugar, a large amount of energy is used.
U.S. Pat. No. 5,411,594 discloses a two-stage plug-flow reactor for continuous saccharification of lingocellulosic biomass. In the method disclosed in the above US patent, biomass is saccharified using the two-stage plug-flow reactor, and thus the saccharification is performed with high efficiency. However, there are disadvantages in that, because two identical reactors are used, the volume of the system is large, and a large amount of energy is used to mix highly viscous sugar.
Accordingly, the present inventors have made extensive efforts to solve the above-described problems, and as a result, have found that, when a mixture of biomass and enzyme is first saccharified in a single tubular first plug-flow reactor (PFR) unit, and then distributed into and saccharified in a second multi-tubular PFR unit comprising a plurality of PFRs, each having a diameter smaller than that of the single-tubular PFR unit, a high concentration of a sugar compound can be obtained without having to use an additional mixer, and investment in a saccharification apparatus and power consumption can be reduced, thereby completing the present invention.